1. Field of the Invention
The present invention relates to a non-halogen-based polyarylate resin having excellent flame-retardancy and ecofriendliness compared to conventional resins or resins containing a halogen-based flame-retardant.
2. Description of the Related Art
Synthetic polymers have been widely used in various fields, for example, for manufacture of plastics, rubbers, fibers, etc. Since most polymer resins have high flammability, attempts have been made to improve the flame-retardancy of the polymer resins. Flame-retardant resins have been prepared by adding small-sized flame-retardant molecules to a polymer resin or by taking a part of polymer backbone with flame-retardant molecules. Halogenated molecules such as brominated aromatic compounds have been used to improve flame-retardancy of polymers. Brominated aromatic flame-retardants have been used to manufacture a variety of plastic products such as computers, fibers, furniture, and construction materials. However, toxic materials such as dioxin generated by the use of halogenated flame-retardants have been accumulated in our environments, and thus the use of halogenated flame-retardants has been restricted, and there is a need to develop non-halogen-based flame-retardants. Furthermore, since halogenated flame-retardants generate hydrogen chloride gas or hydrobromic acid gas while burning, the use of the halogenated flame-retardants are not suitable for airtight space such as planes and ships. In addition, a large amount of an inorganic non-halogen-based additive such as aluminum hydroxide is required to obtain sufficient flame-retardancy which makes it difficult to maintain mechanical properties of a polymer.
An ideal flame-retardant resin is a non-halogen-based resin that has high thermal stability, low combustion heat and low heat release rate (HRR), and does not release toxic gas. Polymers having low flammability generally produce a large amount of char by heat to form a fireproof layer on the surface of the polymers so that the polymers are inhibited from burning since flammable gas generated by the heat is blocked. The char can be formed by mixing an char providing additives such as composite materials.
The HRR of the material is an intrinsic property indicating flammability of a polymer. The HRR can be measured using various calorie measuring methods. Recently, a pyrolysis combustion flow calorimetry (PCFC) has been developed to measure HRR using a small amount of a sample. The PCFC measures heat release capacity and a total heat release capacity of the polymer. The heat release capacity depends on oxygen consumption and determined by heating rate. The heat release capacity that is defined as a maximum calorie produced by a unit weight is an intrinsic property of a material and known as a major index to predict flammability (See, Richard N. Walters, Richard E. Lyon, Journal of Applied Polymer Science, 87(3), 548-563, 2002).
Although an aromatic polyarylate prepared by bisphenol-A and phthalic acid is well known as a high functional engineering plastic and widely used, the heat release capacity (HRC) of the aromatic polyarylate is 359 J/gK indicating high flammability. An aromatic polyarylate containing 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene (BPC) that is known as a self-extinguishing polymer is transparent and has excellent mechanical properties and high flame-retardancy with a heat release capacity (HRC) of 21 and 29 J/gK and 50 to 55% char forming capability (Macromolecules, 39(10), 3553-3558, 2006). However, since BPC-containing polyarylate resins emit hydrogen chloride gas at high temperature, they have limitation for mass-production or for industrial products.
Recently, it has been reported that aromatic polyarylate resins containing 4,4′-bishydroxydeoxybenzoin (BHDB) showed low HRR. It has been reported that the BHDB, like BPC, is aromatized by heat to form char (Macromolecules, 39(10), 3553-3558, 2006). Even though BHDB-containing polyarylate resins have low HRR of 100 J/g-K or less measured by pyrolysis combustion flow calorimetry this is not satisfactory enough.
Thus, there is a need for the development of a polyarylate resin that has excellent flame-retardancy and is safe from environmental aspect.